Metal plating with a heated hydrocarbon solution of a group via metal carbonyl



United States Patent METAL PLATING WITH A HEATED HYDROCAR- BON SOLUTIONOF A GROUP VIA METAL CAR- BONYL Carl Berger, 18 Cooke-Road, Lexington,Mass. No Drawing. Continuation of application Ser. No.

819,561, June 11, 1959. This application Sept. 21,

1962, Ser. No. 225,370

'7 Claims. (Cl. 117-113) This application is a continuation ofapplicants abandoned application Serial No. 819,561, filed on June 11,1959.

This invention relates to a method for coating surfaces with group VIAmetals and more particularly to a method invoving depositing upon asurface, an adherent metal film, said metal film being formed from groupVIA metal carbonyls dissolved in a solvent, either liquid or solid.

Various systems have been used to put a molybdenum, tungsten, orchromium surface on various metallic or nonmetallic substrates. Includedin these are metal spraying, electrophoretic deposition, sputtering andvacuum techniques. High temperatures and slow deposition limit the usesof metal spraying and electrophoretic deposition. The well known vacuumtechniques produce quite thin films and are subjected to low productionlevels, batch production and severe size limitations.

The decomposition of group VIA carbonyl compounds is recorded in theliterature. For instance, I. J. Lander (U.S.P. 2,671,739, March 9,1954), discusses the vapor phase decomposition of molybdenum, tungsten,and chromium carbonyls. Other gas phase decompositions have also beendescribed by Powell (vapor plating). Gas phase decompositions have neverattained practical industrial usage since systems must be tightly sealedagainst atmospheric contamination, constant pressure conditionsmaintained and gas flow rates strictly controlled. Moreover, manyproblems exist in vaporizing decomposable materials and in almost allcases carrier gases must be provided to give direction to the flow ofthe decomposable gas. All additives to the gas stream, in order tomodify metal films produced, must be volatile and flow rates strictlycontrolled. The substrate to be plated must be heated and prepared inthe closed system which also leads to many limitations and engineeringproblems, some of which are insurmountable without resorting toexpensive processes or equipment. Finally, many safety precautions mustbe taken with such systems.

The present invention provides a system where a heat decomposable groupVIA compound in solution in a liquid or solid is put into contact with aheated substrate thereby causing the formation of metal on thesubstrate. The superiority of this technique manifests itself in thefact that the process can be safely performed in an open vessel ifdesired, the chemical and physical nature of the films produced can besimply altered by changing the concentration ofthe heat decomposablemetal carbonyl, the addition of modifying agents to the solvent, and thealterationof solution and substrate temperatures before deposition. Thechoice of the proper solvent allows the freshly plated sample and itsvirgin surface to be protected from contamination (e.g. paraffin wax).The above advantages and others to be described cannot be attained byany other technique available for plating mo- "ice sion or suspension ofthe heat decomposable compound in a solvent can be used. Such emulsionor suspension systems are included within the scope of the presentinvention. Additives may be dissolved or suspended in the solvent toalter the chemical and. physical characteristics of the depositedmolybdenum, tungsten, or chromium surface or to maintain emulsionstability.

It is also possible to use the solid materials which are heatdecomposable into metal without dissolving them or suspending them in asolvent. The use of the material in this manner does not lend itself tothe purposeful alteration of the chemical and physical properties of themetal fihn deposited on various substrates. In addition, many safetyprecautions must be taken with this type of system.

An object of this invention is to provide a method for coating almostany type of surface with a group VIA metal, with the only limitationbeing that the surface itself must be of such a nature that it will notdecompose under the influence of the relatively low temperature requiredin carrying out this method. Thus, surfaces of objects made of metal,glass, suitably hardened clay, variousheat resistant plastics etc., mayall be coated with a thin coating of pure molybdenum, tungsten, orchromium by this process. 1

Another object of this invention is to provide an in expensive means forcoating any surface with a thin coat- 7 ing of a group VIA metal bymeans of subjecting the surfaceto a liquid or solid solution formed of aheat decomposable compound containing a group VIA metal, said compoundbeing dissolved in a liquid solvent or a solid solvent.

'Another object of this invention is to provide an inexpensive means forcoating any surface with a thin coating of either molybdenum, tungsten,or chromium which can be used as an intermediate coating for thedeposition of metals by conventional means or the deposition ofnonmetals or plastics, where a group VIA metal is a preferred substrateto improve adhesion.

These and other objects and advantages of this inven tion will becomeapparent upon reading the following description.

I have now found a process for the deposition in solvent medium of agroup VIA metal on a surface which comprises generally the contacting ofa group VIA metal carbonyl, capable of decomposing under heat toliberate a group VIA metal, in a solvent for said compound with asurface or substrate, While maintaining at least a portion of saidcompound at a temperature of at least in its heat decomposition range.

My invention further includes a process for the deposition in solventmedium of either molybdenum, tungsten, or chromium on a surface whichcomprises the placing of a group VIA metal carbonyl compound, that canbe de- 1 composed in the presence of heat, in a solvent for saidcompound; heating the resulting solution to a temperature slightly belowthe heat decomposition range of said compound; heating the said surfaceto a temperature above about the heat decomposition range of saidcompound; and contacting the said heated-compound with said heatedsurface.

In addition, I have found new molybdenum, tungsten and chromiumcompositions formed on a surface by a method which comprises: contactinga group VIA metal carbonyl compound, capable of decomposing under heatto liberate a group VIA metal, in a solvent for said compound with saidsurface, while maintaining said. compound at a temperature of at leastin its heat decomposition range.

The production of group VIA metal films on various substrates is of muchpractical value. Increased corrosion resistance, oxidation resistance,and superior surface hardness are some of the results obtained by thistechnique. Non-electricity conducting materials such as glass andceramics may be made electrically conductive by depositing the precedingmetal films .on them by my "process. Metal films deposited on variousmetals by my technique may serve as intermediate coatings upon whichother metals such as chromium may be electrodeposited or deposited inany other conventional manner. These metal films may also be produced onglass vessels by my process to produce decorative efiects since films ofhigh gloss are produced on glass.

It is found that any group VIA metal carbonyl capable of decomposingunder heat to liberate metal, which can be dissolved or suspended in asolvent medium, can be used to produce metal films on given substrates.Due to the restrictions of cost, availability, safety, and thetemperature to which the substrates may be heated, it is found thatmolybdenum carbonyl, tungsten carbonyl and chromium carbonyl arepreferred compounds for use. These materials decompose into molybdenum,tungsten, and chromium respectively upon reaching their ultimatedecomposition temperature.

Although it is possible to use pure group VIA metal carbonyls to depositmolybdenum, tungsten, and chromium films, I have discovered that the useof a solvent medium is preferred because of its many advantages. Thesafety of a solvent system is far superior, for instance. Corrosion andengineering problems are minimized and handling problems are aleviated.Without solvent, closed systems containing inert gases must be used andconsiderable caution exercised.

The use of the solvent system yields greater economy since thedecomposition of metal carbonyl, in excess of that needed to produce afilm, is lessened since the metal carbonylis molecularly dispersedthroughout the solvent which dissipates the heat evolving from thesubstrate to be plated.

Unexpectedly, I have found that the state of molecular aggregation ofthe metal carbonyl differs from that found, either in the gas state orthe solvent free solids, when the said metal carbonyl is dissolved in asolvent medium. This is caused by the interplay of the molecularattractive forces of the metal carbonyl and the solvent. These forceswill vary with concentration, temperature, the particular solvent, andthe particular group VIA metal carbonyl used. The net result of thesefactors is that the chemical and physical conditions under which thegroup VIA metals will deposit on various substrates will and does differfrom gas state decomposition or decomposition of the solvent freesolids. For instance, it has been found unexpectedly that thedecomposition of molybdenum carbonyl starts at a lower temperature in aparafiin wax solvent than when it is decomposed in the solvent freestate. For 7.5 percent by weight solution of molybdenum carbonyl inparaffin wax, the difference is about 20-30 degrees centigrade. 4

Another advantage of the use of the solvent state is that the group VIAmetal carbonyls may be dissolved in hot solvents which solidify uponcooling (e.g. paraffin wax) thus providing a convenient handling formfor soldering and other applications where a stable solid heatdecomposable source of either molybdenum, tungsten, or chromium may berequired.

In general, solid and liquid state solventsare useful, especially thehydrocarbons.

Materials which may be used as solvents are higher alkanes, aromatics,and paraflins, which are stable and boil at temperatures greater thantlhe decomposition range of the metal carbonyl compound to bedecomposed.

Typical of such solvents are n-dodecane, l,2,3,4-tetramethylbenzene,Tetralin, naphthalene, l-methyl naphthalene, diphenyl-anthracene,parafiin distillate, parafiin wax and petrolatum (Vaseline). Solventmediums which may not be used are concentrated nitric acid, concentratedsodium hydroxide solutions, fluorine, bromine, and iodine.

The use of various minor components in the solvent medium causesmodification, where desired, of the physical and chemical properties ofthe metal film deposited. Such agents are wetting agents (to promoteadhesion), oxidizing and reducing compounds. Typical of these arecalcium phenyl stearate, polydimethylsiloxane, lead soaps, Na S Ohydrogen peroxide (anhydrous), KMnO LiAlH H 0 peracetic acid, andothers. These important modifications cannot be achieved in either gasstate or solvent free solid state deposition of metal from group VIAmetal carbonyl compounds.

Surfaces on which molybdenum, tungsten, and chromiurn can be depositedsuccessfully are copper, iron, steel, aluminum, as well as alloys of thepreceding and other metals. In addition, films of these metals can bedeposited on glass, ceramics, and other inorganic substrates. Organic orinorganic plastics or resins, which may be heated without decomposing,to above the decomposition temperature of the metal carbonyls' may alsobe utilized. Some phenolics, epoxy resins, and halogenated materialsfall into this class.

' The handling of solvent systems of the metal carbonyls is similar tothe handling of solvent free compounds except that the conditions arefar less stringent.

The group VIA metal carbonyl used is dissolved in the appropriatesolvent and the substrate, heated in any conventional fashion, isbrought into contact with the liquid and a metal film is formed on thissubstrate. The substrate is allowed to cool and is then rinsed with acleaning solvent which will remove the residual metal carbonyl and bathsolvent. Such a cleaning solvent may be heptane or other lower alkanessuch as pentane. a solvent such as paraffin wax is used as a solvent,the plated substrate may be removed immediately since the coolingparafiin solidifies, thus protecting the newly plated surface fromoxidation or other contamination.

One procedure typical of the soldering stick approach which may be usedis to allow the plating bath to remain at room temperature and to heatthe article to be plated sufliciently high, so that when it contacts theliquid or solid bath, it can raise enough of the surrounding metalcarbonyl to its decomposition temperature to produce a film of metal onthe article. Preferably, the plating bath is raised to slightly belowits decomposition temperature or range and the heated article is thensubmerged. This has the advantage of using lower temperatures for thearticle to be plated which can therefore prevent physical and chemicaldeterioration of said article and allow a greater range of articles tobe used.

The plating bath may also be made to flow past an article or manyarticles heated to the proper temperature so that they may decompose theplating liquid flowing by. Finally, the metal carbonyl dissolved in asolid solvent such as paraffin wax, may be formed in stick form to beused to solder heated terminals or other connections. Heated parafiinwax solution may be caused to flow onto a surface, solidify, and thenthe surface may be heated, causing a deposit of metal to form thereon.

The temperature at which decomposition occurs for various solutions ofthe metal carbonyls, Mo(CO) W(CO) Cr(CO) will vary with the solvent. Ihave found that the temperatures from about C. through about C. areoperative. For molybdenum carbonyl solutions, the efiective operatingrange of decomposition is about 120-160 C.; for tungsten carbonyl aboutISO-C; for chromium carbonyl about ll0150 C. The solution in which theseranges were established is 5-7 percent by weight solution of metalcarbonyl in paraffin Wax. The most effective operating temperature ineach case is around the middle of the range, of temperatures. At the lowend of the range decomposition occurs given substrate is a matter of afraction of a second to a few seconds and deposition continues untilinsufiicient heat is available from the substarate to continue thedecomposition. The higher the temperature diflferential betweenthesubstrate and the plating solution (presuming that the platingsolution is near its decomposition point) the faster will the depositionoccur. It is also clear that the thickness of the coat is a directfunctionof the time that the heated specimen is kept in contact with theplating solution, said specimen having enough heat to continueproduction of metal film on its surface.

Films of thicknesses from .0001 inch to .001 inch can be deposited onone immersion. By varying the time of immersion and by repeatingimmersions, thinner and thicker films can be produced. An analysis byspectograph of typical deposited films reveals that they comprisesubstantially pure group VIA metals with slight amounts of carbide andoxide contaminants.

Coatings deposited by my process are free of atmospheric contaminationand can be protected after removal from a bath by utilizing a paraffinwax solvent or allowing to cool within the bath. The metal deposited bythis process is extremely active, probably active enough to serve as acatalytic surface. The chemical nature of the metal films can be variedby the addition of small quantities of modifiers to the solvent used.Therefore, small amounts of impurities may be purposely added or theentire metal film may be converted to a molybdenum, tungsten, orchromium derivative, as, for example, to ,molybdenum carbide or tungstenoxide. None of the systems reported heretofore has the flexibility forproducing the above variations andany attempt to do so is met withextermely difiicult technical and economic problems.

Because of the chemically pure and active nature of the deposited film,this film can be used as' an intermediate coating upon which othermetals such as copper or nickel may be deposited by electro-deposition,vacuum deposition, or other conventional means. The use of the metalfilm or coating as an intermediate may serve to improve adhesion of anoutermost layer of metal, prevent diflusion of'outermost layers of metalinto the base metal, and provide greater corrosion and heat resistance.

The following examples illustrate the novel processes and compositionsof the present invention:

Example 1 In grams of parafl'ln wax, maintained at 70-80 C.,

0.5 gram of Mo(CO) were dissolved. Heating of the Example 2 The sameprocedure as Example 1 was followed. A piece of porous ceramic (1.0" x1.0" x 1.0") was heated to about 200 C. and immersed in the molybdenumcarbonyl solution. A thin dark coating of molybdenum about 0.0002 inchin thickness was formed. The metal 7 film was dark since it deposits outas a finely subdivided metal. If this plated sample is heated, the metalfilm assumes a grey metallic like appearance indicating a coalescence ofthe molybdenum particles.

Example 3 The same procedure as Example 1 was followed. A piece of glass(1.0" x 1.0" x 0.1") was heated to about 175 C. and inserted in thesolution. A silver black coating of molybdenum deposited on the glass ofthickness 0.0005 inch.

' Example 4 Example 5' The same procedure was followed as Example 1except that a 7.5% by weight solution of molybdenum carbonyl in parafiinwax was used instead of-a 5% solution. A piece of steel shim (2.0" x 0.1x 0.5"), a piece of glass (0.5" x 0.5" x 0.1"), and a 1.0" steelnailwere heated and dipped into solution. The results were as follows:

Steel shim (one dip), dark metallic sheen 0.0007" Glass (one dip),silver black metallic sheen 0.0005" -Nail (four dips), blue-blackcoating 0.001"

Example 6 A 5.0% by weight solution of molybdenum carbonyl in liquidparaflin wax was poured into a cylindrical mold and allowed to cool. Asoldering stick resulted. A piece of glass was heated to 300 C. and thestick stroked across the surface. This turned a poor electricalconductor into a good electrical conductor.

Example 7 Utilizing a procedure similar to Example 1 a 5% by weightsolution of W(CO) in parafiin wax was maintained at -150 C. and samplesof material heated and inserted therein. .The results were as follows:

Temper- Thick- Material ature, Description ness,

0. inches Dark coating 0. 0002 150 Dark spotty coating 0. 0001 200-Mirror-like coating- 0. 0003 195 Lustrous black c0ating 0. 0003 225Black coating 0. 0003 200 Black coating 0.0002 195 Dull grey metallicfilm 0. 0002 Grey and black film 0. 0001 198 Black coating 0. 0003 Avariety of useful purposes were served by the above. The glass andceramic specimens were electrically nonconductive before deposition butcarried current readily after tungsten was deposited thereon. Inaddition the steel samples such as the nails and steel shims obtainedextremely hard and heat resistant costs of tungsten.

Example 8 Using exactly the procedure of Example 6, a tungsten solderingstick was produced and used to join two heatedelectrical wires, therebyallowing current to flow between two electrical circuits.

Example 9 0.2 gram of chromium carbonyl, 0.3 gram of tungsten carbonyl,and 0.25 gram of molybdenum carbonyl are dissolved in 10 grams ofVaseline. The temperature of the solution is raised to 105 C. and asteel shim, heated to 7 230 C. is thrust into the solution. A black bluecoating results which is an alloy of molybdenum, tungstemand chromium.The coated steel shim was placed in a nickel plating bath and nickelplated thereon.

Example 10 The procedure of Example 7was followed except that 0.25 gramof calcium phenylstearate was added to the solution. On testing theadhesion of the tungsten to the steelshim by a tape peel test, itappeared that the adhesion of the tungsten to the steel substrate wasimproved by the presence of the surface active agent.

In conducting the general process of this invention, the surface to becoated must be of sulficiently high temperature to raise that portion ofthe bath, which comes into direct contact with the surface, above 120 C.for Cr(CO) 140 C. for Mo(CO) and 160 C. for W(CO) all of which aredissolved in a 50-75% by weight solution in parafiin wax. To do this,when these solutions have been preheated to a temperature slightly belowthe heat decomposition range of the metal carbonyls, respectively, thesubstrate or surface must be heated to a minimum of 140 C. for C'r(CO)150 C. for Mo(CO) and 160 C. for W(CO) respectively. It can be concludedfrom my results that using various solvents will result in a variance ofthe decomposition point of the metal carbonyls. In addition, sufiicientvariation of concentration of the metal carbonyls in various solvents,both liquid and solid, will affect the continuity, porosity, andthickness of the film deposited. This has enabled me to produce metalcoatings having accurately controlled characteristics.

As the concentration of the heat decomposable compound is lowered thedistance between successively decomposing molecules is lengthened andless overlapping of deposited metal atoms i likely to occur.Accordingly, the film is less continuous and greater gaps will alsoresult, yielding increased porosity. Since fewer molecule are in a givenheated volume, fewer will be deposited and a thinner film will result.Inversely, increased concentration will result in greater continuity andthickness.

Moreover, I have observed that combinations of the three metalcarbonyls, in solution give a composite which deposits alloys ofmolybdenum, tungsten, and chromium. This deposition is accomplished byusing the above three metal carbonyls dissolved in paraffin distillate,parafiin wax, Vaseline or other suitable solvents such as higher alkanesand aromatics.

A particular advantage of using solvent systems is that the metalcarbonyls are more safely handled in solution and engineering problemsfor production equipment are simpler. Another important advantage isthat upon removal from the plating bath and cooling a protective solventcoat (solid paratfin wax) can be utilized, if desired, that remains andprotects the metal plated substrate against oxidation, for example.

At the point'of decomposition, that portion of the bath decomposes whichhas reached the decomposition temper-' ature and deposits metal on thesurface. From the examples, it can be seen that the, exact temperatureof the surface may be varied in causing deposition of the metal film, solong as it is somewhat above the decomposition temperature of the metalcontaining compound in solution.

After the initial flash of metal, the coating may be thickened byleaving the object in the bath for an additional lengthof time. However,the substrate must be sufiiciently hot so that its outermost surface,which is now either Mo, W, or Cr is also above the decompositiontemperature of that portion of the bath with which it now comes intocontact. The thickening of the coating will stop either at the pointthat the object is removed from the bath or at the point where theoutermost surface drops below the decomposition temperature of the metallcarbonyls in the bath.

The object to be coaisd i usually dipped into .the bath.

8 However, the soldering approach of Examples 6 and 8 have been usedfrequently.

The bath itself is pre-heated to a point slightly below itsdecomposition temperature. For example, a typical plating bath may bepreheated to about C. Thus, the surface to be coated need be raised onlyslightly above the temperature of decomposition of the bath since thesurface has only to raise that portion of the bath with which it comesinto contact a few degrees (i.e. about 30- 40 degrees centigrade) tocause decomposition and deposition of metal thereon.

As can be seen, another advantage of this process for coating surfacesis that the surfaces need be heated only to a relatively low temperatureand the process takes place very quickly with a relatively inexpensivebath.

Although it is desirable to carry out the coating process in an inertatmosphere, that is, an atmosphere containing no oxygen and no carbondioxide, the method is operative under atmospheric conditions, but amore chemically pure coating is obtained in an inert atmosphere.

It is observed therefore that my invention provides a simple, economicalmethod for producing pure or modified films of-molybdenum, tungsten, andchromium (Examples 1, 7, and 9). In addition, soldering sticks forproviding electrical connections have been produced (Example 6),non-electrical conductors have been made conductive (Example 7), anddecorative tungsten films have been produced (Example 7, glass). Heatresistance and hardness can be provided by the use of the depositedtungsten film-to protect steel (Example 7). The techniques use as anintermediate coating for electroplating (Example 9) has beendemonstrated. I

This invention'may be further developed within the scope of thefollowing appended claims. Accordingly, it is desired that the foregoingdescription be read as being merely illustrative of an operativeembodiment of this invention and not in a strictly limiting sense.

Having fully described the method herein, I now claim:

1. A process for the deposition in solvent medium of a group VIA metalon a surface which comprises: placing a group VIA metal carbonylcompound, capable of ,decomposing under heat to liberate said metal, ina hydrocarbon solvent for said compound, said solvent being stable atand boiling at temperatures greater than the heat decompositiontemperature of said compound; heating the resulting solution to atemperature .below but not morethan about 40 C. below the minimum heatdecomposition temperature of said compound in said solvent and heatingthe said sur-faceto a temperature above about the minimum heatdecomposition temperature of said compound; and immersing said heatedsurface in said heated solution to effect deposition of the metal onsaid surface.

2. The process of claim 1 wherein the group VIA metal carbonyl compoundis selected from the group consisting of molybdenum, tungsten, andchromium carbonyls.

3. The process of claim 1 wherein said Group VIA metal carbonyl compoundcontains an oxidizing agent to oxidize the metal deposited upondecomposition of said Group VIA metal carbonyl compound.

4. The process of claim 1 wherein said Group VIA metal carbonyl compoundcontains a reducing agent to reduce any oxidized metal deposited upondecomposition of said Group VIA metal carbonyl compound.

5. The process of claim 1 whereinsaid' Group VIA metal carbonyl compoundcontains a wetting agent.

6. A process for the deposition in solvent medium-of a group VIA metalon a surface which comprises'z placi-ng a group VIA metal carbonylcompound, capable of decomposing under heat to liberate said metal, in ahydrocarbon solvent for said compound; heating the resulting solution toa temperature slightly below the heat decomposition temperature range ofsaid compound in said solvent but sufficiently below the decompositiontemperature to prevent volatilization and heating the said surface to atemperature above about the heat decomposition temperature of saidcompound; and placing said heated surface 9 in said heated solution toeffect deposition of the metal on said surface.

7. A process for the decomposition in solvent medium of a group VIAmetal on a surface which comprises: placing a group VIA metal carbonylcompound, capable of decomposing under heat to liberate said metal, in ahydrocarbon solvent for said compound, said hydrocarbon solvent beingselected from the group consisting of alkanes and aromatics; heating theresulting solution to a temperature slightly below the heatdecomposition temperature range of said compound in said solvent but notmore than about 40 C. below the minimum heat decomposition temperatureof said compound in said solvent and heating the said surface to atemperature above about the heat decomposition temperature of saidcompound; and immersing said heated surface in said heated solution toeflFect deposition of the metal on said surface.

References Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTSFrance. Germany. Germany.

' Germany.

Germany. Germany. Great Britain. Switzerland.

RICHARD D. NEVIUS, Primary Examiner. 20 W. L. JARVIS, AssistantExaminer.

1. A PROCESS FOR THE DEPOSITION IN SOLVENT MEDIUM OF A GROUP VIA METALON A SURFACE WHICH COMPRISES: PLACING A GROUP VIA METAL CARBONYLCOMPOUND, CAPABLE OF DECOMPOSING UNDER HEAT TO LIBERATE SAID METAL, IN AHYDROCARBON SOLVENT FOR SAID COMPOUND, SAID SOLVENT BEING STABLE AT ANDBOILING AT TEMPERATURES GREATER THAN THE HEAT DECOMPOSITION TEMPERATUREOF SAID COMPOUND; HEATING THE RESULTING SOLUTION TO A TEMPERATURE BELOWBUT NOT MORE THAN ABOUT 40*C. BELOW THE MINIMUM HEAT DECOMPOSITIONTEMPERATURE OF SAID COMPOUND IN SAID SOLVENT AND HEATING THE SAIDSURFACE TO A TEMPERATURE ABOVE ABOUT THE MINIMUM HEAT DECOMPOSITIONTEMPERATURE OF SAID COMPOUND; AND IMMERSING SAID HEATED SURFACE IN SAIDHEATED SOLUTION TO EFFECT DEPOSITION OF THE METAL ON SAID SURFACE.